PRESIDENTS ADDRKSS. G29 



in one thousand yeai*s the proportion of carbon dioxide in the 

 air would, apart from the regulating effect of the sea, be doubled, 

 and the percentage would then be 0*06, a proportion which it is 

 considered would render the atmosphere almost unfit for con- 

 tinued respiration. As the result of direct experiment it is con- 

 cluded that before the proportion of carbon dioxide rose to 0'031 

 per cent, the sea would absorb it as fast as it was produced, 

 " and, owing to the large volume required to bring the ocean 

 into equilibrium with the air, it is probable that at the expira- 

 tion of the thousand years the proportion of carbon dioxide in 

 the air would not be more than 3'5 vols, per 10,000," which is 

 0035 per cent. So far as the products of the life and decay of 

 living organisms are concerned, it may be safely concluded that 

 by these agencies there is returned to the air the same amount 

 of carbon dioxide as is withdrawn, for the sum total of organic 

 life remains practically unaltered from year to year. 



In considering the influence of atmospheric constituents on 

 living organisms it is interesting to note some observations made 

 by Dr. A. Marcacci,* who has shown that, when the nitrogen in 

 the air is replaced by hydrogen, animals placed therein soon die, 

 not from any poisonous effect of the hydrogen, but simply because 

 of the much greater thermal conductivity of that gas. The death 

 of the animals is in fact due to the increased loss of heat, which 

 the organism is unable to maintain, though the effort to do so is 

 evidenced by a greatly increased absorption of oxygen and 

 evolution of carbon dioxide. 



Vast quantities of water are condensed around the cold polar 

 regions of the earth, giving rise to the accumulations of ice which 

 permanently cap the poles. The opinion was at one time widely 

 held that there must be prodigious aggregations of ice at the 

 poles, because where the ice never melts there seemed no limit 

 to the possibilities of its accumulation, and it was even considered 

 probable that a world-wide deluge might be caused when the 

 mountain of ice became so great as to overbalance, and in falling 



* Nature, June 30, 1904, 201. ^-< ^^ p 



42 





